南海永署礁泻湖1680年来微型腹足类丰度变化的环境意义

永署礁南永3井记录了近1680年来礁泻湖腹足类遗壳的沉积变化，其中腹足类丰度变化尤为显著，存在三个高丰度区和相间的三个低丰度区，全样单一的粉砂沉积，表明丰度的变化与底质类型无关，而高分异度显示了一部分腹足类遗壳为水动力搬动的结果，腹足类丰度与沉积速率的对比表明，高沉积速率和低沉积速率以及波动的沉积环境不利于腹足类的发展，而适中的沉积速率和稳定的沉积环境将是腹足类发展的有利因素，发现环境的变化大约以400－600年为周期，1459－1680年间为环境动荡期，腹足类为低丰度，1081－1459年间为环境稳定期，腹足类丰度高；559－1081年间为沉积速率急剧变化期，腹足类为低丰度，1－559年间沉积速率非常稳定，腹足类十分发育。

ENVIRONMENTAL IMPLICATION OF MICROGASTROPOD ABUNDANCE VARIATION IN THE YONGSHUJIAO REEF LAGOON, SOUTH CHINA SEA DURING THE LAST 1 680 YEARS

Core 3 of the Yongshujiao reef lagoon records sedimentary variation of minute gastropods during the last 1 680 years and especially unfolds conspicuous variation in gastropod abundance, shown by alternative occurrence of both the three high abundance and three low abundance. Monotonous fine sand sediment of whole core probably indicates that the gastropod abundance variation did not depend on sedimental substrates and the high diversity of species may imply that some of shells should be the result of tidal current's transportation. Comparison of gastropod abundance with sedimentary rate shows that too high sedimentary rate and very low sedimentary rate as well as unstable sedimentary environment make against development of lagoon gastropods. Moderate sedimentary rate and stable sedimentary environment are favorable to the development of lagoon gastropods. Environmental change periods of 400-600a are recognized as follows: unstable in 1 459-1 680 a BP and low gastropod abundance; stable in 1 081-1 459a BP and high gastropod abundance; sharp turbulence in 559-1 081a BP and low gastropod abundance; very stable in 1-559 and very high gastropod abundance.